* PokerStars offers bonuses regularly, but not very often. Maybe once every three months or so (I believe the last one was in November).
* You need to deposit the whole amount you want money for at once. You can't deposit it in increments of $50; you'd only get bonus for the first deposit. If you have the discipline (and the cash) to only play for as much as you've set up a goal to play for each month, then it might make sense to make a bigger deposit right off the bat, as you would get a bigger total bonus that way.
* If you don't play enough hands to get your bonus the first month, no problem - you can keep playing until it's cleared. It, as Fish pointed out, never expires (like, for instance, the FullTilt bonus does).
* It has a maximum deposit of $600, meaning that even if you had a $10k bankroll, you'd still only get bonus for the first $600. I also believe - although I haven't checked lately - that Stars only allows you to deposit $600 at a time.
* You can deposit, wait 48 hours (minimum) and then withdraw all of your money again. If you at some later point decide to redeposit, your bonus will still be active, and you can work on it then. You don't have to finish it all at once. If you need to play 5000 hands to clear it, you can deposit now, play 2000 hands, withdraw all your cash and return in 6 months, make a new deposit and play the remaining 3000 then. You'll still get the same bonus you were eligible for originally.
Hope that clears it up.
